In various instances it may be useful to provide a duct with a variable flow geometry for conveying material. One potential application for such a duct may be in the separation of cotton from green bolls and other debris. For example, in a harvester such as a cotton stripper, cotton and other material (e.g., green bolls and other debris, which may be generally referred to as “trash”) may be gathered from a field and routed to a separation duct. The separation duct may direct the cotton and other material through one or more turns in the duct between the duct entrance and the duct exit, in order to deposit material into an attached basket or other receptacle. As the material moves through these turns the lighter cotton may trace paths of generally smaller radii than the radii of the paths of heavier green bolls and other debris. This may beneficially allow for separation of the heavier green bolls and other debris from the lighter cotton.
Depending on the characteristics of the gathered material (e.g., cotton, green bolls, and other debris), however, turns for separating material (as described above) may also present a choke point for the duct. For example, although a tighter turn in a duct may lead to more significant separation of the heavier debris (i.e., because the debris cannot trace a small enough radius to follow the turn), this may also lead to clogging of the duct as cotton and other material bunches together at the relatively tight restriction of the turn. It may therefore be useful to provide a turn in a separation duct that is tight enough to provide appropriate material separation, while not so tight as to result in clogging. The flow of material through a given duct, however, may vary depending on a variety of factors including the type of pick-up header utilized for harvesting, the speed of travel of the harvesting vehicle, the type and yield of the cotton, the arrangement of the relevant field, and so on. Accordingly, one particular duct geometry (e.g., a separation curve of particular cross-section and curvature) may be well-suited to prevent clogging under one set of conditions but not under others.
In this light, it may be useful to provide a duct of variable geometry, in order to provide for effective separation of cotton from other material under a variety of conditions. Further, such a variable geometry duct may be useful in a variety of other applications, including other material separation operations.